The invention relates to a displaying measuring instrument with a digital measuring circuit for the magnitude to be displayed, in which the display of the value of that magnity is obtained by selective change of appearance of certain visual display elements of a display panel.
Traditionally, measuring instruments have for a long time been designed as pointer instruments. In such instruments, the magnitude to be measured is applied to a drive means such as a moving coil, which positions the pointer along a calibrated scale in correspondence with the value of the quantity to be measured. Such pointer instruments have the advantage that an approximate impression of the measuring value can be obtained at a glance, and that any change with time of the measuring value can be followed easily. In case of the occurrence of rapid fluctuations of the measuring value too, a good indication of the mean value can be obtained and, provided that the fluctuations are not too fast in comparison to the inertia of the measuring instrument, it is also possible to obtain a rough impression of the presence and magnitude of such fluctuations. A further advantage is the absence of active components in as far as no extreme sensitivity is required. However, disadvantages are the sensitivity for mechanical defects, the small accuracy of the measuring instrument itself, the need for a very careful reading, in which it is always necessary to make an estimate of the precise position of the pointer with respect to the scale, and the very limited possibility of reading fluctuations of the measuring value.
Later, measuring instruments with digital read-out have been developed, in which the value of the measuring quantity is displayed directly in numerals. Advantages thereof are that the accuracy of the measuring instrument can be increased almost indefinitely, that no estimate is necessary for reading the measuring instrument, that the measuring instrument is comparatively insensitive to mechanical defects and that by a combination of standard units, any desired measuring function and measuring range can be obtained. Also, it is possible without difficulties, to obtain an indication of the polarity of the measuring quantity and of any exceeding of the range. However, disadvantages are that the reading becomes virtually impossible for rapidly fluctuating measuring values, since one or more display numerals will change rapidly in that case, whereby these numerals can be read hardly or not at all. Also, it is difficult to obtain an impression of the course of a slowly changing measuring value, since the speed with which and the direction in which the measuring value changes, can be derived only from the time which passes between the changes of the displayed numerals and the sense in which these numerals change respectively. For fluctuating measuring values it is virtually impossible, to read the range within which the measuring value fluctuates.
Because of these advantages and disadvantages, both kinds of measuring instruments found an application area of their own. Since the circumstances in which a measuring instrument will be used cannot always be predicted with any certainty, measuring instruments of either type are often used in circumstances in which the disadvantages inherent to the type of measuring instrument concerned are of great practical importance.